Supporting structural tissues in the body including tooth, bone, skin, tendon, etc. often become weak or brittle as a result of disease or injury. Some collagenous natural materials like mussel byssal threads are significantly tougher and more durable than the healthiest tendons of their vertebrate counterparts. Such superior performance is likely to be endowed by improvements in molecular design. Two suggested improvements in byssus are A. the amalgamation of byssal collagen with fibroin-like and or resilin like domains, and B. the complete coating of the structure by a natural sealant containing a Dopa-protein and catechol oxidase. In this proposal, 3 goals have been experimentally delineated: 1) The silk- and resilin-like domains of byssal collagens will be characterized biochemically and by standard recombinant DNA methodology; 2) the sealant catechol oxidase will be sequenced, localized in situ using immunogold labelling, and studied kinetically using peptides modelled after natural substrates; 3) Molecular interactions among the precursors in nascent byssal threads will be examined using a bifunctional reversible cross- linker in combination with acid-urea polyacrylamide gel electrophoresis, electroblotting to polyvinylidene difluoride membranes, and matrix assisted laser desorption ionization mass spectrometry of blotted proteins.